1. Technical Field
The present invention relates generally to an improved data processing system and, in particular, to a method, apparatus, and computer program product for enhancing performance in a data processing system. Still more particularly, the present invention provides a method, apparatus, and computer program product for testing differential clock or oscillator signals in a data processing system.
2. Description of Related Art
A microprocessor is a silicon chip that contains a central processing unit (CPU) which controls all the other parts of a digital device. Designs vary widely but, in general, the CPU consists of a control unit, an arithmetic and logic unit (ALU) and memory (registers, cache, RAM and ROM) as well as various temporary buffers and other logic. The control unit fetches instructions from memory and decodes them to produce signals which control the other part of the computer. This may cause the control unit to transfer data between memory and ALU or to activate peripherals to perform input or output. A parallel computer has several CPUs which may share other resources such as memory and peripherals. In addition to bandwidth (the number of bits processed in a single instruction) and clock speed (how many instructions per second the microprocessor can execute), microprocessors are classified as being either RISC (reduced instruction set computer) or CISC (complex instruction set computer).
An oscillator clock is a circuit within a microprocessor that creates a series of pulses that pace the microprocessor's electronic system. The oscillator clock synchronizes, paces and coordinates the operations of the microprocessor's circuit. For differential signals, such as those used for oscillator distribution between oscillator generator circuits and user chips, to detect if one leg of a differential pair is broken is always a problem. Due to the nature of this differential signal, the function will still be partially available even with one leg broken.
One currently available technique to detect a broken leg of a differential pair is to add two single-ended receivers to the main differential receiver. One of these additional single-ended receivers is connected to the positive leg of the differential pair, and the other single-ended receiver is connected to the negative leg of the differential pair. The three output signals of the three receivers can then be observed by standard missing pulse detectors. The problem with this scheme is that standard missing pulse detectors need several cycles to detect a missing pulse, and in some situations the single-ended receiver is generating inverted signals, which cannot be detected by standard missing pulse generators.
Therefore, it would be advantageous to have an improved method, apparatus, and computer program product for detecting a broken leg of a differential pair. The wiretest system of the present invention tests differential clock or oscillator signals, and detects failures due to a broken leg within one cycle.